Core for web material

ABSTRACT

A core that is adapted to receive web material such as a wound film roll includes inner and outer coaxial cylinders joined together by a ring plate that extends perpendicular to the longitudinal axes of the inner and outer cylinders. A plurality of radially disposed ribs are positioned between and connected to the inner and outer cylinders. At least one projection is provided on the core at one of various places such as the inner surface of the outer cylinder or the outer surface of the inner cylinder. The projection increases frictional resistance between the mold core and the molded core, thereby ensuring the mold core will be ejected with the core from the mold cavity. The core is manufactured from a resin composition comprising 70 to 30 wt. % of polypropylene resin having a melt index of 10 to 60 g/10 minutes, a bending elastic modulus of more than 8,000 kg/cm 2 , an Izod impact strength of more than 2 kg.cm/cm and a Rockwell hardness of more than 70 R, 30 to 70 wt. % of linear low density polyethylene resin having a melt index of 3 to 50 g/10 minutes, a density of 0.910 to 0.935 g/cm 3 , an Olsen rigidity of more than 1,500 kg/cm 2  and a Shore hardness of more than 40 D, more than 0.01 wt. % of a lubricant and more than 0.01 wt. % of an antioxidant.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a core for a photographic photosensitive webmaterial including roll films and roll papers, such as the negative orpositive films for movie, negative or positive microfilms, long 35 mmroll films (J 135), the films for phototype setting, the films forcomputer and the papers for computerized type-setting system, and aresin composition suitable for it.

2. Description of Prior Art

The above photographic photosensitive web materials such as the negativeor positive films for movie is sold and used in a state coiled around acore. Most conventional cores for web material were made ofthermoplastic resin, particularly high-impact polystyrene resin wheresynthetic rubber (mainly butadiene rubber) is blended or polymerizedwith polystyrene resin. The shape of a conventional core for webmaterial is shown in FIGS. 6 and 7.

In the core for web material shown in the above drawings, an outercylinder 1 and an inner cylinder 2 having almost the same length as theouter cylinder are disposed so that their axes are made consistent witheach other. Both cylinders 1, 2 are joined by a ring plate 3 disposedperpendicular to the axis of the core at their centers and by eightpairs of ribs 4 disposed at the same position as each other through thering plate 3. The ribs 4 have almost the same shape as the section ofthe circular channel formed by the cylinders 1, 2 and the ring plate 3,and they are disposed in radial directions of the cylinders 1, 2 atregular intervals. Resin-injecting gates are disposed at the center ofthe edges of the eight ribs 4 on one side, and the gate remainder 6remain at the respective corresponding positions. Moreover, the innercylinder 2 is provided with an engaging channel 8 for engaging a pawl orthe like of the shaft of a moving picture camera or a moving pictureprojector in the axial direction, and the outer cylinder 1 is providedwith a slit channel 7 for inserting an end of the film in the axialdirection.

The inventor developed a core for web material where the gate portionsare moved to the centers of respective sector portions of the ring plate3 partitioned by the cylinders 1, 2 and the ribs 4, 4, as shown in FIG.4, in order to improve compressive strength (Japanese Utility ModelKOKAI No. 61-128256). Moreover, the inventor also developed another corefor web material where the compressive strength is improved and theweight is decreased by cutting off the ribs 4 from each free end portionas shown in FIG. 3 (Japanese Utility Model KOKAI No. 61-86367).

Other known cores for web material, include a core where the flanges areintegrated (Japanese Utility Model KOKAI No. 49-18536) and a core whereone of the flanges is made detachable and thereby the long film can beplaced in the coiled state (Japanese Utility Model KOKOKU No. 59-24025).

In the conventional cores for web material such as mentioned above, allfaces including the inner surface of the outer cylinder and the outersurface and the inner surface of the inner cylinder as well as the outersurface of the outer cylinder are made flat.

In such conventional cores, molded cores were liable to remain on theside of cavities. Since the cores remaining in the cavities could not beejected by a stripper, they caused ejecting trouble. Moreover, weld linewas strongly formed, and decreased compressive strength, droppingstrength and the like.

Moreover, the cores made of the aforementioned resin were soluble inorganic solvents, and the shape were liable to be damaged. Since theresin contained synthetic rubber, the core was inferior in transparency,and it was expensive.

SUMMARY OF THE INVENTION

An object of the invention is to provide a core for web material that iseasily ejectable from the cavity of an injection molding machine, andexcellent in moldability.

Another object of the invention is to provide a core for web materialwherein a weld line hardly occurs, and wherein appearance and strengthare improved.

Another object of the invention is to provide a resin compositionsuitable for a core for web material, and excellent in dimensionalaccuracy, chemical resistance, physical strength including compressivestrength, dropping strength and surface strength, and injectionmoldability by not generating a weld line.

The present invention has been made in order to achieve such objects andis based upon the findings that, when the contact area with the cavitywas greater than with the mold core, the molded core was liable toremain on the side of the cavity due to the greater friction resistancewith the cavity than with the mold core. Another finding is that theweld line occurred on the opposite side to the gate due to the delayedinflux of the resin caused by its inferiority in fluidity.

In the core for web material of the invention, the above problems havebeen solved by providing one or more projections at a portion of thecore for web material to be contacted with the mold core, and therebyensuring the ejection of the molded core because the friction resistancebetween the molded core for web material and the mold core is greaterthan the friction resistance between the molded core and the moldcavity. Thus, the core for web material of the invention comprises acore made of a thermoplastic resin for web material molded by injectionmolding which comprises an outer cylinder, an inner cylinder disposed sothat its axis is aligned with (the axes are coaxial) the axis of theouter cylinder, a ring plate joining both cylinders disposed around thecenter of both cylinders perpendicular to the above axis and plural ribsjoining both cylinders disposed in the radial directions from the axissubstantially symmetrical about the above ring plate. One or moreprojections are formed at least at a part of the portion of the core forweb material to be contacted with the mold core at the time of injectionmolding.

The present invention also provides a resin composition which hasachieved the above object suitable for the above core for web material,comprising 70 to 30 wt. % of polypropylene resin having a melt index of10 to 60 g/10 minutes, a bending elastic modulus of more than 8,000kg/cm², an Izod impact strength of more than 2 kg·cm/cm and a Rockwellhardness of more than 70 R, 30 to 70 wt. % of linear low densitypolyethylene resin having a melt index of 3 to 50 g/10 minutes, adensity of 0.910 to 0.935 g/cm³, an Olsen rigidity of more than 1,500kg/cm² and a Shore hardness of more than 40 D, more than 0.01 wt. % of alubricant and more than 0.01 wt. % of an antioxidant.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a core for web material embodying theinvention.

FIG. 2 is a front view thereof.

FIG. 3 is an enlarged sectional view taken on line 3--3 of FIG. 2.

FIG. 4 is a front view of another core for web material embodying theinvention.

FIG. 5 is an enlarged sectional view taken on line 5--5 of FIG. 4.

FIG. 6 is a front view of a conventional core for web material.

FIG. 7 is a sectional view taken on line 7--7 of FIG. 6.

FIG. 8 is a perspective view of a core for web material according toanother embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The projection is formed for the purpose that the friction resistancebetween the core for web material and the mold core is made greater thanthe friction resistance between the core for web material and the cavityso that the molded core for web material does not remain in the cavity.Therefore, the size, shape, number and the like of the projection may bevaried within the extent capable of achieving the above condition.However, the number is preferably more than one, and for example, theprojection may be several lines formed in parallel, spots, stripes, orthe like. The projection may be formed at least at a part of the portionto be contacted with the mold core, and for example, it may be formed atone or more parts of the inner surface of the outer cylinder, the innerand outer surfaces of the inner cylinder, and the ribs.

The outer cylinder is the portion on which is wound the web material,and when the outer surface is made rough, pressure marks or abrasionmarks occur in the photographic photosensitive web material coiledaround the core. Therefore, it is preferable that the outer surface ofthe outer cylinder is flat and smooth, or the irregularities on theouter surface be than several micrometers in height.

The inner cylinder is the portion to be inserted into the shaft of theapparatus which uses the web material.

The inner cylinder is disposed so that the axis is coaxial with the axisof the outer cylinder, and joined to the outer cylinder around thecenter of both cylinders through one piece of the ring plate disposedperpendicular to the above axis. As a result, the section of the joinedportion becomes H-shape. The ring plate may be provided with windows andthe like, for example, at the portions between respective ribs.

The plural ribs are disposed in the radial directions from thelongitudinal axis and substantially symmetrically about the above ringplate, and they also join both cylinders. The symmetrical arrangement ispreferable in the balance of resin flow. The shape of the ribs may beany known shape. All ribs need not necessary to be identical in shape,thickness and the like. The number of the ribs is decided according tothe size, strength and the like of the core for web material, and it isusually 2 to 32 pieces.

The thickness of each portion may be uniform or partly thickened orthinned.

The ring plate is partitioned into sector portions by the ribs and bothcylinders, and each resin-injecting gate portion is preferably disposedaround the center of each sector portion on one side of the ring plateor around the center of the edge of each rib, because the treatment ofthe gate mark is not necessary. The number of the resininjecting gatesis, in general, made even in view of the balance of resin flow.

Various modifications may be added to the core for web materialaccording to its use. In the case of a core for movie film, themodifications include a channel for engaging a pawl of the shaft of amoving picture projector, a slit channel for inserting an end of thefilm and flanges for holding the coiled film.

The shapes, the sizes, the thicknesses and the like of respectiveportions mentioned heretofore is decided according to the kind, length,size and required properties of the web material, and may be identicalwith any known core, other than the projection mentioned previously.Various indications such as company name, trade name, mold number andthe like can be cut in the ring plate.

In the core for web material of the invention, the projection fits inthe indentation of the mold forming the projection of the core, andthereby friction resistance is increased. As a result, the molded corefor web material is ejected while attached to the mold core.

The material forming the core may be any thermoplastic resin. However,polypropylene resin, polystyrene resin, ABS resin and the like arepreferable, and more preferable resin contains more than 50 wt. % ofhigh-impact polystyrene resin excellent in dimensional accuracy, rareoccurrence of bottom sink mark, great physical strength andinexpensiveness. The thermoplastic resin may contain various additives,such as lubricant, antistatic agent, light-shielding material, whitepigment, color pigment, color dye, antioxidant, metal powder, higherfatty acid, metal salt of fatty acid and coupling agent.

However, the present invention provides a particularly suitable resincomposition suitable for the core of web material, which comprises aparticular polypropylene resin, a particular linear low densitypolyethylene (L-LDPE) resin, a lubricant and an antioxidant.

The melt index (MI, ASTM D-1238) of the polypropylene resin is 10 to 60g/10 minutes, preferably 20 to 50 g/10 minutes, more preferably 30 to 40g/10 minutes. When the MI is less than 10 g/10 minutes, the resinfluidity is worse. As a result, weld lines greatly occur, and droppingstrength and compressive strength decrease. Besides, sink marks greatlyoccur, and appearance is inferior. When the resin is used for a core forphotographic photosensitive web material, pressure marks occur in ribportions. Moreover, injection moldability is inferior, and molding cycleis elongated. Even though the resin temperature is raised, short shot isliable to occur. Sink marks are great, and cooling time is elongated.While, when the MI is beyond 60 g/10 minutes, physical strengthdecreases. Surface hardness and rigidity are small, and burrs andstringiness are liable to occur.

The bending elastic modulus (ASTM D-790) of the polypropylene resin ismore than 8,000 kg/cm², preferably more than 9,000 kg/cm², particularlypreferably more than 10,000 kg/cm². When the bending elastic modulus isless than 8,000 kg/cm², the resin is soft. In the case of blending itwith L-LDPE resin in order to improve Izod impact strength, compressivestrength is insufficient.

The Izod impact strength (ASTM D-256, at 23° C.) of the polypropyleneresin is more than 2 kg·cm/cm, preferably more than 3 kg·cm/cm,particularly preferably more than 4 kg. cm/cm. When the Izod impactstrength is less than 2 kg·cm/cm, the blending amount of the L-LDPEresin must be increased in order to improve Izod impact strength. As aresult, the resin remaining at gate and stringiness frequently occur,and weld lines greatly occur because the resin fluidity is worse.

The Rockwell hardness (ASTM D-785) of the polypropylene resin is morethan 70 R, preferably more than 80 R, particularly preferably more than90 R. When the Rockwell hardness is less than 70 R, the resin powder byabrasion and scratches occur in the channel for engaging the core with apawl of a developing apparatus, a moving picture projector or a winder,the slit for inserting an end of a web material and the flanges forholding the coiled web material, and the trouble that the resin powderadheres to the web material occurs. Particularly, in photographicphotosensitive roll films, such as film for movie and microfilm, andcomputerized type-setting paper, when the resin powder adheres to them,the merchandise values are lost.

The polypropylene resin having the properties mentioned above may behomopolypropylene resin or a copolymer resin of propylene and anα-olefin having a number of carbon atoms of 2 to 8, such aspropylene-ethylene random copolymer or propylene-ethylene blockcopolymer. In view of preventing whitening, preferable polypropyleneresin is propylene-ethylene random copolymer resin having a propyleneunit of 90 to 99.5 wt. % and an ethylene unit of 10 to 0.5 wt. %,particularly a propylene unit of 93 to 99 wt. % an ethylene unit of 7 to1 wt. %.

In the case of employing any type polypropylene resin, the meanmolecular weight ratio (Mw: weight average molecular weight / Mn: numberaverage molecular weight) measure by gel permeation chromatography is1.5 to 8, preferably 2 to 6, more preferably 2.5 to 5 in view of thebalance among the improvement in dimensional accuracy, the prevention ofsink marks, the increase of rigidity, the security of strength,injection moldability and the like. When the mean molecular weight ratiois less than 1.5, polymerization ability is worse and injectionmoldability is inferior.

The polypropylene resin preferably contains a nucleating agent in viewof rigidity, wear resistance, injection moldability, such as thepreventions in stringiness, resin remaining at gate and burrs, theimprovement in mold separability, and the like. The nucleating agent maybe an organic nucleating agent, an inorganic nucleating agent or amixture thereof, and an organic nucleating agent is preferred.

Though the polymerization method of polypropylene resin is notrestricted, the vapor phase polymerization method is preferable in viewof little mean molecular weight distribution resulting a narrowmolecular distribution, a good dimensional accuracy and little sinkmarks and inexpensiveness. Catalysts to form a stereoregularpolypropylene resin are preferred in view of securing the necessaryproperties.

The content of the polypropylene resin is 70 to 30 wt. %. When thecontent is beyond 70 wt. %, the occurrence of sink marks, the decreaseof physical strength and the increase of mold shrinkage are problems.While, when the content is less than 30 wt. %, rigidity, wear resistanceand injection moldability are inferior.

The L-LDPE resin is blended in order to increase Izod impact strengthsharply and to improve dimensional accuracy and sink marks. The MI ofthe L-LDPE resin (ASTM D-1238) is 3 to 50 g/10 minutes, preferably 5 to30 g/10 minutes, particularly preferably 7 to 20 g/10 minutes. When theMI is less than 3 g/10 minutes, resin fluidity is inferior to result theoccurrences of weld lines and short shot. While, when the MI is beyond50 g/10 minutes, the resin composition is inferior in dropping strength,rigidity, stringiness, gate remainder wear resistance and ESCR (ASTMD-1693).

The density (ASTM D-1505) of the L-LDPE resin is 0.910 to 0.935 g/cm³,preferably 0.915 to 0.930 g/cm³, particularly preferably 0.917 to 0.928g/cm³. When the density is less than 0.910 g/cm³, rigidity isinsufficient. Wear resistance is inferior, and polymerization propertiesare inferior resulting expensive. While, when the density is beyond0.935 g/cm³, dropping strength is inferior.

The Olsen rigidity (ASTM D-747) is more than 1,500 kg/cm², preferablymore than 1,800 kg/cm², particularly preferably more than 2,100 kg/cm².When the Olsen rigidity is less than 1,500 kg/cm², compressive strengthis insufficient. As a result, when the winding pressure is great bywinding a long web material, the core deforms.

The Shore hardness (ASTM D-2240) is more than 40 D, preferably more than45 D, particularly preferably more than 50 D. When the Shore hardness isless than 40 D, the problems occur similar to the case that the Rockwellhardness of the polypropylene resin is less than 70 R.

The mean molecular weight of the L-LDPE resin is similar to the case ofthe polypropylene resin.

The L-LDPE resin is a copolymer of ethylene and α-olefin and it has alinear structure having short branches. The number of carbon atoms ofthe α-olefin is 3-13, preferably 4-8, more preferably 6-8, and theexamples are butene-1, 4-methylpentene-1, hexene-1, heptene-1 andoctene-1. Suitable ethylene content of L-LDPE is 85-99.5 mol. %, i.e.α-olefin content is 0.5-15 mol. %, and preferable ethylene content is90-99.5 mol. %, i.e. α-olefin content is 0.5-10 mol. %. The density isusually in the range of 0.87-0.95 g/cm³, (ASTM D-1505). Such a L-LDPEresin is manufactured by solution method, slurry method, vapor phasemethod, or modified high pressure method. Examples of L-LDPE resin are"G-RESIN", (trade name, UCC), "DOWLEX" (trade name, Dow Chemical Co.,Ltd.), "STAMILEX" (trade name, DSM), "SUCLEAR" (trade name, Dupont deNemour, Canada), "MARLEX" (trade name, Phillips Co., Ltd.), "ULTZEX" and"NEOZEX" (trade name, Mitsui Petroleum Chemical Industries Co., Ltd.)and "NISSEKI LINIREX" (trade name, Nippon Petrochemicals Co., Ltd.).

The lubricant is added in order to improve injection moldability, moldseparability, resin fluidity and the like. The content of the lubricantis more than 0.01 wt. %, preferably 0.03 to 2 wt. %, particularlypreferably 0.05 to 0.5 wt. %. When the content is less than 0.01 wt. %,the separability of the core from the mold. Static electricity is liableto generate, and the surface is liable to be damaged. However, when thecontent is too much, the injected amounts vary due to screw slip.Plasticization ability is insufficient. Bleeding out of the lubricantincreases, and developing trouble occurs due to the adhesion of thelubricant to the photosensitive web material. When the resin compositionis used for the package of photographic photosensitive materials, themaximum content not affecting the photosensitive materials adversely is2 wt. %.

The lubricant includes:

Oleic acid amide lubricants; "ARMOSLIP-CP" (Lion akzo Co., Ltd.),"NEWTRON" and "NEWTRON E-18" (Nippon Fine Chemical Co., Ltd.), "AMIDE-O"(Nitto Kagaku K.K.), "DIAMID O-200" and "DIAMID G-200" (Nippon KaseiChemical Co., Ltd.), "ALFLOW E-10" (Nippon Oil and Fats Co., Ltd.), etc.

Erucic acid amide lubricants; "ALFLOW P-10" (Nippon Oil and Fats Co.,Ltd.), "NEWTRON S" (Nippon Fine Chemical Co., Ltd.), etc.

Stearic acid amide lubricants; "ALFLOW S-10" (Nippon Oil and Fats Co.,Ltd.), "NEWTRON 2" (Nippon Fine Chemical Co., Ltd.), "DIAMID 200"(Nippon Kasei Chemical Co., Ltd.), etc.

Bis fatty acid amide lubricants; "BISAMIDE" (Nippon Fine Chemical Co.,Ltd.), "DIAMID-200 BIS" (Nippon Kasei Chemical Co., Ltd.), "ARMOWAX-EBS"(Lion Akzo Co., Ltd.), etc.

Silicone lubricants; Dimethylpolysiloxanes, etc. (Sinetsu Chemical Co.,Ltd., Toray Silicone Co., Ltd.), etc.

Alkylamine lubricants; "ELECTROSTRIPPER TS-2" (Kao Corp.) etc.

Preferable lubricants include the fatty acid amide lubricants having anumber of carbon atoms of 8 to 50, preferably 15 to 35. Two or morelubricants may be combined.

The antioxidant is added in order to prevent yellowing and coloring ofthe resin. The content of the antioxidant is more than 0.01 wt. %,preferably 0.03 to 1 wt. %, particularly preferably 0.05 to 0.5 wt. %.When the content is less than 0.01 wt. %, continuous injection for along time is impossible, because the yellowing of the resin occurs.However, in the case of a core for photographic photosensitive webmaterial, when the content is too much, troubles occur in the quality,such as fogging and sensitivity variation. The maximum content notaffecting the photographic photosensitive materials adversely is 1 wt.%.

Suitable antioxidants are phenol antioxidants, sulfur-containingantioxidants, phosphorus-containing antioxidants and the like. Thephenol antioxidants includen-octadecyl-3-(3',5'-di-t-butyl-4'-hydroxyphenyl)propionate,2,6-di-t-butyl-4-methylphenol, 2,6-di-t-butyl-p-cresol (BHT),2,2'-methylenebis(4-methyl-6-t-butylphenol),4,4'-thiobis(3-methyl-6-t-butylphenol),4,4'-butylidenebis(3-methyl-6-t-butylphenol),stearyl-β-(3,5-di-4-butyl-4-hydroxyphenyl)propionate,1,1,3-tris(2-methyl-4-hydroxy-5-t-butylphenyl)butane,1,3,5-trimethyl-2,4,6-tris(3,5-di-t-butyl-4-hydroxybenzyl) benzene,octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl) propionate and tetrakismethylene-3(3',5'-di-t-butyl-4'-hydroxyphenyl)propionate methane. Thesulfur-containing antioxidants include dilauryl-3,3'-thiodipropionate,dimyristyl-3,3'-thiodipropionate, laurylstearylthiodipropionate,distearyl-3,3'-thiodipropionate and ditridecyl-3,3'-thiodipropionate.The phosphorus-containing antioxidants include trinonylphenylphosphiteand triphenylphosphite. Particularly effective antioxidants are BHT, lowvolatile high molecular weight phenol antioxidants ("Irganox 1010","Irganox 1076", trade names of Ciba-Geigy A.G., "Topanol CA", trade nameof I.C.I., etc.), dilaurylthiodipropionate, distearylthiodipropionate,dialkylphoshpate, etc. Particularly preferable antioxidants are phenolantioxidants. Two or more antioxidants may be combined.

When carbon black is added. The antioxidation effect is synergisticallyexhibited.

The resin composition of the invention preferably further contains anucleating agent in view of the improvements of rigidity, injectionmoldability, transparency, wear resistance and heat resistance, and thedecrease of molding troubles such as stringiness, gate remainder andburrs.

The resin composition of the invention may contain other knownadditives. Representative other additives usable for the resincomposition are illustrated as follows:

(1) Plasticizer; phthalic acid esters, glycol esters, fatty acid esters,phosphoric acid esters, etc.

(2) Stabilizer; lead compounds, cadmium compounds, zinc compounds,alkaline earth metal compounds, organic tin compounds, etc.

(3) Antistatic agent; cation surfactants, anion surfactants, nonionsurfactants, ampholytic surfactants, etc.

(4) Flame retardant; phosphoric acid esters, phosphoric acid esterhalides, halides, inorganic materials, polyols containing phosphor, etc.

(5) Filler; alumina, kaolin, clay, calcium carbonate, mica, talc,titanium oxide, silica, etc.

(6) Reinforcing agent; glass lobing, metallic fiber, glass fiber, glassmilled fiber, carbon fiber, etc.

(7) Coloring agent; inorganic pigments (Al, Fe₂ O₃, TiO₂, ZnO, Cds,etc.), organic pigments (carbon black) dyes, etc.

(8) Blowing agent; inorganic blowing agents (ammonium carbonate, sodiumhydrogen carbonate), organic blowing agents (nitroso compounds, azocompounds), etc.

(9) Vulcanizing; vulcanization accelerator, acceleration assistant, etc.

(10) Deterioration preventing agent; ultraviolet absorber, antioxidant,metal deactivator, peroxide decomposing agent etc.

(11) Coupling agent; silane compounds, titanium compounds, chromiumcompounds, aluminum compounds, etc.

(12) Antiblocking agent; silica, diatomaceous earth, talc, silicate,aluminum silicate, magnesium silicate, calcium carbonate, higher fattyacid polyvinyl esters, n-octadecylurea, dicarboxiylic acid ester amide,N,N'-dioleyloxamide, etc.

(13) Various thermoplastic resins, rubbers, etc.

In addition, a chlorine absorbent, a light-shielding material and thelike may also be blended.

The resin composition is a light weight and excellent in injectionmoldability, appearance, dropping strength, solvent resistance,transparency, processibility, wear resistance, dimensional accuracy, andlittle molding troubles such as sink marks, gate remainder, stringiness,weld lines, twist and deformation, and nevertheless, it has aflexibility.

Though the use of the resin composition is not restricted, it issuitable for cores for various photographic photosensitive webmaterials, including the core for web material of the invention, such asfor video tape, audio tape, movie film, film for phototype setting, filmfor computer, computerized type-setting paper and the like. The core isparticularly suitable for the positive film for movie and positivemicrofilm.

The core for web material is molded by injection molding includingintermold vacuum injection molding.

Flanges and other parts may be attached to the core for web material,and the core may be printed or labeled.

Since the ejection of the core for web material is improved, injectionmoldability is improved. The resin fluidity is improved, and therebyweld lines do not form. The appearance and the physical strength arealso improved. By using the resin composition described herein, theprocessibility, appearance and physical strength are further improved,and injection molding cycle can be shortened.

EXAMPLES

A core for web material embodying the invention is shown in FIGS. 1 to3.

As shown in the drawings, the core is formed of an outer cylinder 1, aninner cylinder 2, a ring plate 3 and eight pairs of ribs 4, 4, . . . 4.The length of the inner cylinder 2 is the same as the outer cylinder 1,and the inner cylinder 2 is disposed so that its axis is aligned withthe axis of the outer cylinder 1. Thus, the inner and outer cylinders1,2 are coaxial. The ring plate 3 is disposed perpendicular to the abovecommon axis, and joins both cylinders 1, 2 at their center. The ribs 4are all the same shape except one pair disposed at the slit 7 forinserting the film and the engaging channel 8. Except for the oneaforementioned pair, the ribs 4 are of a rectangular shape having theirfree edge cut into a reverse trapezoidal shape through their fulllength. The pair of ribs 4 disposed adjacent the slit 7 and the channel8 is shortened by the projections of the slit 7 and the engaging channel8 that project toward the rib 4. Each pair of ribs 4 is disposedsymmetrics about the ring plate 3 in the radial directions from the axisat regular intervals, and is joined to both cylinders 1, 2 and the ringplate 3. That is, the ring plate 3 is partitioned into eight sectorportions. Resin-injecting gates (not illustrated) are disposed at thecenter of respective sector portions, and gate remainder 6 remainsthere. The inner cylinder 2 is provided with an engaging channel 8 forengaging a pawl of the shaft of a moving picture camera or a movingpicture projector in the axial direction, and the outer cylinder 1 isprovided with a slit channel 7 for inserting an end of the film in theaxial direction. In such a core, the projection 5 for increasing thefriction resistance to the mold core (not illustrated) is formed on theinner surface of the outer cylinder 1 on the opposite side to theresin-injecting gate portions. The projection 5 is composed of threering lines disposed parallel with respect to each other at equalintervals in the circumferential direction of the outer cylinder 1.

Another core for web material embodying the invention is shown in FIGS.4 and 5. The core is the same as the above core, except that each rib 4is rectangularly shaped and the projection 5 comprised of three ringlines is formed on the outer surface of the inner cylinder 2 instead ofthe inner surface of the outer cylinder 1.

As seen in FIG. 8, the projections for increasing the frictionalresistance to the mold care can take the form of spots 5'. In theembodiment shown in FIG. 8, the spots 5' are formed on the inner surfaceof the outer cylinder 1.

Subsequently, various properties of three examples of the core of theinvention were measured together with a comparative core and aconventional core.

Core of the Invention I

The core of the invention I is the core for 35 mm movie film 2000 feetin length, and is made of a high-impact polystyrene resin ("Styron",Asahi Chemical Industries). It has a shape shown in FIGS. 1 to 3. Theoutside diameter of the outer cylinder is 76.2 mm, and the insidediameter of the inner cylinder 2 is 25.9 mm. The length of bothcylinders 1, 2 is 34.5 mm. The size of each rib 4 is 15 mm in length×21mm in width. The angle between the surface of each cylinder 1 or 2 andthe oblique cut line of the rib 4 is 30 degrees, and the length of thecut part parallel with the ring plate 3 is 10 mm. The thickness of theouter cylinder 1 is 2.1 mm, the thickness of the inner cylinder 2 is 2.0mm, the thickness of the ring plate is 2.2 mm, and the thickness of therib 4 is 2.0 mm. The height of each ring line of the projection 5 is 0.3mm, and the width is 0.5 mm. The distance between respective ring linesis 2.5 mm.

Core of the Invention II

The core of the invention II is the same as the core of the invention I,except that the ribs 4 are rectangular shaped as shown in FIG. 5 andhave a size of 10 mm in length×21 mm in width.

Core of the Invention III

The core of the invention III is the same as the conventional core,except that the same projection 5 as the core of the invention I isformed.

Comparative Core I

The comparative core I is the same as the core of the invention II,except that the projection 5 is not formed.

Conventional Core I

The conventional core I has a shape shown in FIGS. 6 and 7, and the sizeof the rib 4 is 15 mm in length×21 mm in width.

The measured results are summized in Table 1.

                                      TABLE 1                                     __________________________________________________________________________                 Core of Invention Comparative                                                                          Conventional                                         I     II    III   Core I Core I                                  __________________________________________________________________________    Front View   FIG. 2                                                                              FIG. 4                                                                              FIG. 6                                                                              FIG. 4 FIG. 6                                  Rib shape    FIG. 3                                                                              FIG. 5                                                                              FIG. 7                                                                              FIG. 5 FIG. 7                                  Weight (g)    39     40.6                                                                                44.6                                                                               40     44                                     Weld Line    A     A     B     B      C                                       Injection Moldability                                                                      A     A     A     C      C                                       Compressive Strength (kg)                                                                  363   345   305   328    265                                     Dropping Strength                                                                          A-B   A-B   A-B   B      B                                       Processing of                                                                              Not   Not   Necessary                                                                           Necessary                                                                            Not                                     Gate Remainder                                                                             Necessary                                                                           Necessary          Necessary                               __________________________________________________________________________

Evaluations were carried out as follows:

    ______________________________________                                        A         very excellent                                                                              B        excellent                                    C         practical                                                           ______________________________________                                    

Weld Line: The generation degree of the weld lines in each core wasevaluated by visual observation.

Injection Moldability: Evaluated by the separability of the moldedproduct and the occurrence of molding troubles such as short shot anddeformation such as warp and twist by organoleptics.

Compressive Strength: The maximum value obtained by measuring using acompression tester "Strograph R-Type" manufactured by Toyo SeikiSeisaku-Sho, Ltd.

Dropping Strength: Evaluated by the damaged state of the core coiledwith a 35 mm width positive film for movie 2,000 feet in length droppedfrom 30 cm height by organoleptics.

Core of the Invention IV

The shape of the core of the invention IV is the same as the core of theinvention I, except that the projection 5 is not formed. The resincomposition of the core is composed of 50 wt. % of polypropylene resinwhich is propylene-ethylene random copolymer resin consisting of 96.5wt. % of propylene unit and 3.5 wt. % of ethylene unit having a MI of 38g/10 minutes, a bending elastic modulus of 11,000 kg/cm², an Izod impactstrength of 4.3 kg·cm/cm and a Rockwell hardness of 90 R manufactured byvapor phase polymerization method, 49.7 wt. % of L-LDPE resin which is acopolymer resin of ethylene and 4-methylpentene-1 having a MI of 18 g/10minutes, a density of 0.919 g/cm³, an Olsen rigidity of 2,200 kg/cm² anda Shore hardness of 50 D manufactured by solution polymerization method,0.2 wt. % of BHT as the antioxidant and 0.1 wt. % of oleic acid amide asthe lubricant. The core was molded by a common injection molding usingan injection molding machine with a cold runner at a mold clampingpressure of 100 t. The molding number per once was one.

Core of the Invention V

The shape of the core of the invention V is the same as the core of theinvention II except that the projection 5 is not formed, and the resincomposition is the same as the core of the invention IV.

Core of the Invention VI

The shape of the core of the invention VI is the same as theconventional core I, and the resin composition is the same as the coreof the invention IV.

Core of the Invention VII

The shape of the core of the invention VII is the same as the core ofthe invention II except that the projection 5 is formed on the innersurface of the outer cylinder 1 instead of the outer surface of theinner cylinder 2. The resin composition of the core is composed of 54.4wt. % of the same polypropylene resin as the core of the invention IV,45 wt. % of L-LDPE resin which is a copolymer resin of ethylene and4-methylpentene-1 having a MI of 10 g/10 minutes, a density of 0.925g/cm³, an Olsen rigidity of 2,500 kg/cm² and a Shore hardness of 52 Dmanufactured by solution polymerization method, 0.2 wt. % of BHT as theantioxidant and 0.2 wt. % of 1,3,2,4-di(methylbenzilidene) sorbitol asthe organic nucleating agent, 0.2 wt. % of oleic acid amide as thelubricant.

Core of the Invention VIII

The shape of the core of the invention VIII is the same as the core ofthe invention VII. The resin composition of the core is composed of 55wt. % of the same polypropylene resin as the core of the invention IV,44.5 wt. % of L-LDPE resin which is a copolymer resin of ethylene and4-methylpentene-1 having a MI of 12 g/10 minutes, a density of 0.920g/cm³, an Olsen rigidity of 2,500 kg/cm² and a Shore hardness of 50 Dmanufactured by solution polymerization method, 0.3 wt. % of BHT as theantioxidant, 0.1 wt. % of a phosphor-containing antioxidant and 0.1 wt.% of oleic acid amide as the lubricant.

Comparative Core II

The shape of the comparative core II is the same as the core of theinvention VI, and the core is composed of the same polypropylene resinas the core of the invention VI alone.

Comparative Core III

The shape of the comparative core III is the same as the core of theinvention VI, and the core is composed of the same L-LDPE resin as thecore of the invention VI alone.

Conventional Core II

The shape of the conventional core II is the same as the core of theinvention VI, and the core is composed of the high-impact polystyreneresin ("Styron", manufactured by Asahi Chemical Industries) alone.

Various properties of the above cores, and the results are summarized inTable 2.

                                      TABLE 2                                     __________________________________________________________________________               Core of Invention      Comparative Core                                                                        Conventional                                 IV  V    VI  VII  VIII II   III  Core II                           __________________________________________________________________________    Front View FIG. 1                                                                             FIG. 4                                                                            FIG. 6                                                                             FIG. 4                                                                             FIG. 4                                                                            FIG. 6                                                                             FIG. 6                                                                             FIG. 6                            Rib Shape  FIG. 3                                                                             FIG. 5                                                                            FIG. 7                                                                             FIG. 5                                                                             FIG. 5                                                                            FIG. 7                                                                             FIG. 7                                                                             FIG. 7                            Weight (g) 32.7                                                                              32.7 35.8                                                                              32.6 32.7 32.3 33.1   44.6                            Cost Ratio 62  62   67  62   62   61   66   100                               Necessity of Gate                                                                        No  No   Yes No   No   Yes  Yes  Yes                               Remainder Trimming                                                                       A   A    C   A    A    C    E    C                                 Injection  A   A    A   A    A    A    E    C                                 Moldability                                                                   Sink Mark  B   B    B   B    B    E    B    B                                 Weld Line  B   B    B   B    B    B    D-E  C                                 Transparency                                                                             B   B    B   B    B    A    C    E                                 Dropping Strength                                                                        A   A    A   A    B    E    A    D                                 Solvent Resistance                                                                       A   A    A   A    A    A    A    E                                 Wear Resistance                                                                          B   B    B   A    A    A    C    D                                 __________________________________________________________________________

Evaluations were carried out as follows:

    ______________________________________                                        A:      very excellent                                                                              B:      excellent                                       C:      practical     D:      having a problem                                E:      impractical                                                           ______________________________________                                    

Cost Ratio: The cost ratio of the resin to Conventional core II.

Necessity of Gate Remainder Trimming: "Yes" indicates that packagingwork or developing work was interfered with the gate remainder when thecore was used without trimming the gate remainder, and "No" indicatesthat the above works were not interfered.

Sink Mark: The sink marks in each core was evaluated by visualobservation.

Solvent Resistance: Evaluated by immersing each core in alcohol andtriol.

Wear Resistance: Evaluated by the worn degree of each core after usedfor a long time in a developing apparatus.

We claim:
 1. A core for web material that is fabricated from athermoplastic material and molded by injection molding through use of amold core, comprising:an outer cylinder; an inner cylinder disposedcoaxially with respect to the outer cylinder; a ring plate positionedbetween and joining said inner and outer cylinders, said ring platebeing disposed perpendicular to the longitudinal axes of the inner andouter cylinders and passing through the approximate axial centers of theinner and outer cylinders; a plurality of substantially symmetricallyand radially disposed ribs positioned between and joining the inner andouter cylinders; and projection means formed on an inner surface of theouter cylinder for increasing the frictional resistance between the coreand the core mold, said projection means having a shape that isconfigured different from each of said plurality of ribs.
 2. The core ofclaim 1, wherein said at least one projection includes a plurality ofparallel linear projections.
 3. The core of claim 1, wherein said coreis configured to receive a wound roll of movie film.
 4. The core ofclaim 1, wherein each of said plurality of ribs has a free edge locateddistally from the ring plate, at least a portion of the free edge ofeach rib being recessed inwardly in the axial direction from the nearestend face of the inner cylinder and outer cylinder.
 5. The core of claim4, wherein the recessed portion of each rib is shaped as a substantiallytruncated triangle.
 6. The core of claim 1, wherein said at least oneprojection includes a plurality of spots.
 7. The core of claim 1,wherein said core is configured to receive a wound roll of microfilm. 8.A core for web material that is fabricated from a thermoplastic materialand molded by injection molding through use of a mold core,comprising:an outer cylinder; an inner cylinder disposed coaxially withrespect to the outer cylinder; a ring plate positioned between andjoining said inner and outer cylinders, said ring plate being disposedperpendicular to the longitudinal axes of the inner and outer cylindersand passing through the approximate axial centers of the inner and outercylinders; a plurality of substantially symmetrically and radiallydisposed ribs positioned between and joining the inner and outercylinders; and projection means formed on an outer surface of the outercylinder for increasing the frictional resistance between the core andthe core mold, said projection means having a shape that is configureddifferent from each of said plurality of ribs.
 9. The core of claim 8,wherein said at least one projection includes a plurality of parallelprojections.